The Hantaan virus M-segment glycoproteins G1 and G2 can be expressed independently

Abstract

The two glycoproteins of Hantaan virus (HTV), G1 and G2, are encoded as a continuous single open reading frame in the M segment of the virion RNA. They are believed to be synthesized contemporaneously via a polypeptide precursor which is then processed to yield two glycoproteins, both of which appear in the Golgi complex of the cell. To study the properties of G1 and G2 as separate entities, we have constructed vaccinia virus recombinants which contain the sequences for each glycoprotein individually. Both glycoproteins made from these recombinants appear normal on sodium dodecyl sulfate-polyacrylamide gels compared with HTV products made in virus-infected cells. Interestingly, in the independently expressed G2 recombinant, a stretch of hydrophobic amino acids preceding the mature G2 N terminus appears to contain the signals necessary for translocation across membranes and proper glycosylation; partial deletion of this hydrophobic sequence results in production of an nonglycosylated form of G2. Thus, both G1 and G2 appear able to be expressed in an authentic fashion quite independently of each other, using their own signal sequences. In addition, it appears that the G1 from vaccinia virus recombinants contains the motif(s) necessary for cellular targeting of the HTV glycoproteins, while G2 from vaccinia virus recombinants remains strongly associated with the endoplasmic reticulum. In contrast, cells doubly infected with G1-vaccinia virus and G2-vaccinia virus recombinants show the G2 in a predominantly perinuclear (Golgi-like) distribution, presumably targeted there through association with G1. A carboxy-terminal deletion of G1 (2-43-Vac), which lacks 82 amino acids proximal to the start of the mature G2, retains a Golgi-like distribution.